While I think vote locking things like master resets is acceptable, I don't think anything in the beginning should be vote locked. There's already a lot of hard requirements for the the 13th & 15th prestiges.
While I appreciate the suggestion, I think it's necessary to keep the votes for phoenix. Master resets are a long term goal yes, but in the beginning new players won't look for that cause they don't know about it. They will work with what's in front of them, and so the phoenix prestige helps nudge them to start voting, which is great for server advertisement.
Also phoenix is the last prestige challenge before you can prestige normally, so I wanna make it harder than the rest. You have in-between time to work on your cell, build pop gear, or play on survival while your waiting on votes.