Phillips has signed a new two-year deal to remain at the Liberty Stadium.
The 23-year-old made his Ospreys debut in February 2017 and has made 15 more appearances, scoring three tries.
“I’m really happy to have signed another two years here. It’s a great club and it’s where I want to be,” said Phillips.
“Captaining the ‘A’ team was great for me and a different experience. I really enjoyed it and scoring three tries against the Scarlets was definitely up there as one of the highlights of the season for me!
“Hopefully I can kick on next year and play a bit more senior rugby. Clarkie was an international hooker so it’s great for me to learn from him. We’ve got really good competition in the hooker position which is great for everyone involved as we’ll keep on pushing each other.”
Ospreys head coach Allen Clarke said: “I’m delighted another young Welsh player of the calibre of Ifan, who came late into our system to progress through to the senior squad, has committed to the region.
“Not only is he a quality rugby player, he’s developing as a leader with a deep hunger for success.
“I’m expecting him to continue to progress over the next two years and in turn challenge the more senior hookers in the squad Sam Parry and Scott Otten.”
Phillips follows lock Lloyd Ashley and scrum-half Matthew Aubrey in signing two-year contract extensions.
Fellow Ospreys Harri Morgan, Gareth Thomas, Scott Otten, Nicky Smith, Cory Allen, Dan Evans, Luke Morgan and Tiaan Thomas-Wheeler have also signed new deals.
Ashley said: “It’s nice to have the next two years secure at the Ospreys. I’m delighted to be here.
“I think, however long you are here, you can continue learning. As a professional rugby player I want to play all the time. I can get frustrated at times when I’m not playing, but when you see the quality we’ve got in the second row, it’s nice to be around those players and learning all the time.
“At the moment we’ve got a very good group of people who want to get better, but who also want to enjoy their time here as well. You are around boys you want to spend time with and that’s got to be a highlight for me.”
