As the title says, this combo doesnt work like, the game doesn´t allow me. I read both card texts carefully but whenever I banish Tzolkin with my Phantom of Chaos and copy it´s effects and set a card, nothing happens, I am unable to special summon a lvl 7 or 8 Synchro monster. Don´t know if the criteria is to have the extra field zone free but even if it is free, it still doesnt work. Both cards are out of long but no one uses it like that so wouldn´t be surpsirsed if the bug, if its one, is there for long.
I just Tested it, and it work fine on my end

- Are you on Ygopro Percy?
- Can you provide a Replay? because like that we can't tell you what you could have missed (like an "you cannot special summon" cost/effect or a ruling)