That won't make any difference. If the AP doesn't do AC then the phone isn't even trying to anyway.
The AP announces what it can do and the client associates if it is capable of the minimum compatible rate and security.
Modes and data rates are then adaptive based on errors/retires due to channel conditions,
For the OP,
another factor will be whether a client device makes do with a single antenna (strictly, what types of MIMO it can do). Products are always advertised based on the maximum theoretical rate at 40, 80 or 160MHz, even if these wider channel modes are unsuitable.
If an AP is properly configurable, set 2.4GHz (b/g/n) to 20MHz wide and 5GHz (a/n/ac) to 40Mhz wide (this is really a bond of 2x adjacent 20Mhz channels), as a starting point unless you have e.g. a detached house out of range of neighbouring Wi-Fi.
prompt $P - Invalid drive specification - Abort, Retry, Fail? $G
prlzx on iDNET: ADSL2+ / 21CN at ~4Mbps / 700kbps with IP4/6