Can I do my 90-day report in Chiang Mai if I live in Phuket?

okay you are mixing up two things. That the 3 months AFTER your extension when you show your bank balance happens the same time as your next 90 day report is coincidental.

BUT

IF you have a sheet that tells you when you show up with your updated bank book you do that.

You need to re-arrange your travel to meet the requirements of the visa extension you're on so that means showing up at the immigration office that issued your extension to show your updated bank book.

You cannot..

You do the report in the immigration office that serves the area of where you live. You cannot do it in Chiang Mai if you live in Phuket.

You could do it online but as you have to prove your bank balance, you need to do it personally in Phuket.

If you have an appointment to show your bank balance in Phuket you better do that, or go before your trip and explain to them.

Is the reason you need to show your bank balance because it was required by Phuket Immigration when you obtained your Extension of Stay for retirement?