Can I apply for a 60-day extension at Phuket immigration if my current 90-day COVID extension stamp is from Kanchanaburi?

Hmmm, :/ there is NO 90 day unable to travel due to covid extension :O

There is an "unable to travel due to medical reasons" 90 day extension.

Now the only reason a person would have that extension in their passport would be because they handed their passport and a pile of baht to someone who took it to a province where you don't live and got the extension :O

I think you're gonna run into some real issues when you show up at the Phuket immigration office with a 90 day medical extension from Kanchanaburi in your passport (especially seeing as you didn't live in that province OR go there to get the extension yourself :().

LOOK at the extension stamp you got from Kanchanaburi. IF it's because of covid it will have the "embassy request" clause #2.28 written on it, but if it was because of medical it will have the "medical extension" clause #2.25 written on it somewhere.

Good luck with it,