Assalamualaikum ustaz. Is it sunnah for an imam to announce assolatul jami’ah to the makmum after the iqamah before the obligatory prayer is performed? This confused me greatly, for what I know, the obligatory prayer is performed after calling only adhan and iqamah. Hope for an explanation.
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions and all those who follow his footsteps until the Last Day.
First and foremost, the adhan is sanctioned to call the Muslims for obligatory prayer to be performed in congregation at the mosque. The sanctioning of the adhan happened during the first year of hijrah.  While the origin of the phrases of the adhan is sanctioned from two companions in the time of the Prophet PBUH, where they dreamt of the phrases. They are Abdullah bin Zaid R.A and Umar bin al-Khattab R.A. This is mentioned in a narration in a long hadith, where Abdullah bin Zaid RA said:
لَمَّا أَمَرَ رَسُولُ اللهِ صلى الله عليه وسلم بِالنَّاقُوسِ يُعْمَلُ لِيُضْرَبَ بِهِ لِلنَّاسِ لِجَمْعِ الصَّلاَةِ طَافَ بِي وَأَنَا نَائِمٌ رَجُلٌ يَحْمِلُ نَاقُوسًا فِي يَدِهِ ، فَقُلْتُ : يَا عَبْدَ اللهِ أَتَبِيعُ النَّاقُوسَ ؟ قَالَ : وَمَا تَصْنَعُ بِهِ ؟ فَقُلْتُ : نَدْعُو بِهِ إِلَى الصَّلاَةِ ، قَالَ : أَفَلاَ أَدُلُّكَ عَلَى مَا هُوَ خَيْرٌ مِنْ ذَلِكَ ؟ فَقُلْتُ لَهُ: بَلَى ، قَالَ : فَقَالَ : تَقُولُ : اللَّهُ أَكْبَرُ ، اللَّهُ أَكْبَرُ ، اللَّهُ أَكْبَرُ ، اللَّهُ أَكْبَرُ…رُ
قَالَ : ثُمَّ اسْتَأْخَرَ عَنِّي غَيْرَ بَعِيدٍ ، ثُمَّ ، قَالَ : وَتَقُولُ : إِذَا أَقَمْتَ الصَّلاَةَ ، اللَّهُ أَكْبَرُ اللَّهُ أَكْبَرُ…رُ
“When the Messenger of Allah (ﷺ) ordered a bell to be made so that it might be struck to gather the people for prayer, a man carrying a bell in his hand appeared to me while I was asleep, and I said; a servant of ‘abd Allah, will you sell the bell? He asked; what will you do with it? I replied; we shall use it to call the people to prayer. He said; should I not suggest you something better than that. I replied: certainly. Then he told me to say: Allah is most great, Allah is most great, Allah is most great, Allah is most great (until the end of adhan). He then moved backward a few steps and said: when you utter the IQAMAH, you should say: Allah is most great, Allah is most great (until the end of iqamah).
When the morning came, I came to the Messenger of Allah (May peace be upon him) and informed him of what I had seen in the dream. He said:
إِنَّهَا لَرُؤْيَا حَقٌّ إِنْ شَاءَ اللَّهُ ، فَقُمْ مَعَ بِلاَلٍ فَأَلْقِ عَلَيْهِ مَا رَأَيْتَ ، فَلْيُؤَذِّنْ بِهِ ، فَإِنَّهُ أَنْدَى صَوْتًا مِنْكَ فَقُمْتُ مَعَ بِلاَلٍ ، فَجَعَلْتُ أُلْقِيهِ عَلَيْهِ ، وَيُؤَذِّنُ بِهِ ، قَالَ : فَسَمِعَ ذَلِكَ عُمَرُ بْنُ الْخَطَّابِ ، وَهُوَ فِي بَيْتِهِ فَخَرَجَ يَجُرُّ رِدَاءَهُ ، وَيَقُولُ : وَالَّذِي بَعَثَكَ بِالْحَقِّ يَا رَسُولَ اللهِ ، لَقَدْ رَأَيْتُ مِثْلَ مَا رَأَى ، فَقَالَ رَسُولُ اللهِ صلى الله عليه وسلم : فَلِلَّهِ الْحَمْدُ.
It is a genuine vision, and he then should use it to call people to prayer, for he has a louder voice than you have. So, I got up along with Bilal and began to teach it to him and he used it in making the call to prayer. ‘Umar b. al-Khattab (Allah be pleased with him) heard it while he was in his house and came out trailing his cloak and said: Messenger of Allah. By him who has sent you with the truth, I have also seen the kind of thing as has been shown to him. The Messenger of Allah (May peace be upon him) said: To Allah be the praise.” 
Second, the phrase al-Solah al-Jami’ah (الصَّلَاةُ الْجَامِعَة) is the call to prayer for sunnah prayer to be performed in congregation. This is based on the eclipse incident which occurred during the Rasullullah PBUH as stated in a hadith narrated from Abdullah bin ‘Amru R.Anhuma:
لَمَّا كَسَفَتِ الشَّمْسُ عَلَى عَهْدِ رَسُولِ اللَّهِ صلى الله عليه وسلم نُودِيَ إِنَّ الصَّلاَةَ جَامِعَةٌ
“When the sun eclipsed in the lifetime of Allah’s Messenger (ﷺ) and an announcement was made that the prayer was to be held in congregation.” 
Likewise, it is stated in a hadith narrated from Aisyah R.Anha, she said:
أنَّ الشَّمْسَ خَسَفَتْ على عَهْدِ رَسولِ اللهِ صَلّى اللَّهُ عليه وسلَّمَ، فَبَعَثَ مُنادِيًا: الصَّلاةُ جامِعَةٌ
“There was an eclipse of the sun in the time of God’s Messenger, and he sent one to summon the people to congregational prayer (الصَّلَاةُ الْجَامِعَة).” 
According to this hadith, it is not sunnah to call the adhan to call others to perform the sunnah eclipse prayer. It is enough by calling: al-Solah al-Jami’ah (الصَّلَاةُ الْجَامِعَة).
According to the above query, it is not sunnah for an imam to announce al-Solah al-Jami’ah (الصَّلَاةُ الْجَامِعَة) after the iqamah and before the obligatory prayer is performed. The reason is the call for obligatory prayers has been set to be just the adhan and iqamah, while the al-Solah al-Jami’ah call is for sunnah eclipse prayer as performed by Rasullullah PBUH.
However, it is sunnah for an imam to instruct the makmum to straighten and close the saf. This is based on a hadith narrated from Anas bin Malik RA, where the Messenger PBUH said:
سَوُّوا صُفُوفَكُمْ؛ فإنَّ تَسْوِيَةَ الصَّفِّ مِن تَمامِ الصَّلاةِ.
“Straighten your rows. for the straightening of a row is a part of the perfection of prayer.” 
The same is also stated in a hadith narrated by Anas RA, he said:
أُقِيمَتِ الصَّلاَةُ فَأقْبَلَ عَلَيْنَا رَسُولُ اللهِ – صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ – بِوَجْهِهِ ، فَقَالَ : أَقِيمُوا صُفُوفَكُمْ وَتَرَاصُّوا ؛ فَإنِّي أرَاكُمْ مِنْ وَرَاءِ ظَهْرِي
The iqama had been uttered and God’s Messenger faced us and said, “Make your rows straight and stand close together, for l can see you behind my back.” 
 See Fiqh al-Manhaji, 1/338
 Narrated by Abu Dawud (449)
 Narrated by al-Bukhari (1045)
 Narrated by al-Bukhari (723) and Muslim (433)
 Narrated by al-Bukhari (719) and Muslim (434)