Are you worried y-combinator people might steal a phone…?
Why would anyone with an ounce of sense give these people and their setup anything of value?
OK. A typical key costs, what, $1? Would you hand me all your keys?
You can trust me. The economics of stealing some cheap pieces of metal are pretty silly.
It's just a setup I'd expect from someone in grade 2, not people pretending to be professionals.
I also use my phone for all sorts of security authentication. I wouldn't volunteer it to anyone else for any reason that wasn't an absolute emergency. It's a needless risk without any benefit. I can just keep it in my pocket on silent.
*obvious parody