The seat was vacated by then MP Keshav Prasad Maurya after his election to the Uttar Pradesh Legislative Council.
While the BJP will seek to retain the seat and also increase its victory margin, rival political parties will try to wrest it from the saffron party and send a signal before the 2019 parliamentary elections.
The BJP has fielded Kaushalendra Singh Patel, while the Congress and the SP have given tickets to Manish Mishra and Nagendra Pratap Singh Patel, respectively.
As many as 22 candidates, including nine independents, are in the fray. Among the independents is mafia-turned-politician Atiq Ahmed.
Atiq had been a Lok Sabha member from here in 2004, when he contested the elections on an SP ticket.
Phulpur parliamentary constituency consists of Phulpur, Phaphamau, Soraon (SC), Allahabad North, and Allahabad West assembly segments. Voting will be held on March 11 and the votes will be counted on March 14.
In the 2014 Lok Sabha elections, BJP's Keshav Maurya won from Phulpur with a record margin of 3.08 lakh votes -- the first time when the 'lotus' bloomed in the constituency.
Maurya had bagged 5,03,564 votes, while his nearest rival Dharam Raj Singh Patel (SP) had got 1,95,256 votes.
During a recent election meeting, Mr Maurya had urged the young voters to ensure an electoral win for BJP candidate Patel.
"The people of Phulpur had given me a victory margin which was greater than (that of) Pandit Nehru. My appeal to you is that Kaushalendra Patel's victory margin should be greater than my victory margin," Mr Maurya said during one of his campaigns.
Seeking to galvanise party workers, Mr Maurya said, "Sab Jaaiye Bhool, Yaad Rakhiye Sirf Kamal ka Phool (forget everything, remember only one thing that lotus has to bloom)."
In the 2017 UP Assembly elections, BJP candidates registered wins in Phulpur (Praveen Patel), Phaphamau (Vikramjeet Maurya), Allahabad North (Harshvardhan Bajpai) and Allahabad West (Sidharth Nath Singh), while in Soraon (SC), it was ally Apna Dal (Sonelal) whose candidate Jamuna Prasad Saroj emerged victorious.
Stating that the electoral scenario and caste equation in Phulpur is "significantly in favour of the BJP", a senior party leader told a visiting PTI correspondent that the party has given a ticket to Kaushalendra Singh Patel - who commands at least 60 per cent of the community votes.
Apart from a large section of Patels, Phulpur also has a Pasi community (scheduled castes), who have been traditional voters of the BJP, the BJP leader said.
With ex-MP Atiq Ahmed contesting as an independent, Muslim votes, which the SP was eyeing, is likely to be split.
"Congress candidate Manish Mishra is only trying to encash the name of his father (KN Mishra), who had once contested the Lok Sabha elections, but lost," the BJP leader said.
The party leaders were also of the view that youths (people under 35), who constitute nearly 60 per cent of the electorate, will also play a major role in the by-election.
However, UP BJP spokesperson Manish Shukla said his party was contesting the election on the plank of development.
"The development which the constituency has witnessed in the last four years can easily be compared with the development after 60 years of independence," he said.
He said the BJP constructed a number of railway overbridges, installed solar lights, and has undertaken the widening of roads in the last four years.
"Development in Phulpur is now visible, and this has infused a sense of confidence among the people, who will definitely vote for the BJP," Mr Shukla said.