Praise be to Allah, The Lord of the Worlds; may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Saying or congratulating with a phrase that hasn`t been reported in the Prophetic Sunnah isn`t religiously prohibited. Rather, this is lawful in Islam so long as it doesn`t violate the teachings of Sharia. It isn`t conditioned that supplication should be based on evidence from Sunnah since it was unconditionally stated in the Quran and the Prophetic Sunnah. In this regard, Allah The Almighty says, "When My servants ask thee concerning Me, I am indeed close (to them): I listen to the prayer of every suppliant when he calleth on Me: Let them also, with a will, Listen to My call, and believe in Me: That they may walk in the right way." {Al-Baqarah, 186}. Therefore, we don`t see anything wrong with saying such phrase or linking it with a particular time, and it isn`t permissible to ban it or describe it as a newly introduced innovation (Bid`ah), because it is a supplication. Thus, saying "Jumu`ah Mubaraakah" to a Muslim is supplicating Allah that he has a blessed Friday. This is in addition to the fact that Friday is a blessed day,as the Messenger of Allah said, "The best day on which the sun has risen is Friday. On that day Adam was created, he was admitted to Jannah, and he was expelled therefrom."{Muslim}. Moreover, Friday is a day of celebration for Muslims since Omar Bin Al-Khattaab (May Allah be pleased with him) said, "Friday and the Day of Arafah, thanks to Allah, are days of celebration"{Reported by Tabari in "Jaami` Al-Bayaan}.
In conclusion, we see nothing wrong with this supplication "Jumu`a Mubaraakah". On the contrary, we believe that it increases the bonds of brotherhood amongst Muslims. However, it is worth pointing that this supplication shouldn`t be ascribed to the Prophet (PBUH) since no evidence has been reported, in this regard, in religious texts. And Allah the Almighty knows best.