Hi  @Cogerber 

Thanks for posting here.

Please refer to the following to troubleshoot:

Devices retain LAN IP but cannot access the internet, possibly due to DHCP lease or gateway misconfiguration.
>>>

• Access the main router's management interface and verify the DHCP pool is sufficient (to avoid IP conflicts).
• Confirm that new phones obtain the correct IP, subnet mask, default gateway, and DNS (compare with wired devices).
• Try assigning a static IP to the new phones to check for improvement.

Possible Cause: New phones support Wi-Fi 6 (802.11ax), which may cause compatibility issues when mixed with older devices.
>>>Split the SSIDs for 2.4GHz and 5GHz (e.g., name them “WiFi-2G” and “WiFi-5G”) and prioritize 5GHz for new phones.
Adjust channels:
For 2.4GHz: Use non-overlapping channels like 1, 6, or 11, and set bandwidth to 20MHz.
For 5GHz: Choose less congested channels like 36 or 149, with bandwidth set to 80MHz.

Update Firmware and Drivers
Upgrade the EAP225 to the latest firmware (we have a newer firmware version for EAP225 V3, you can download from TP-Link’s official website).
Check if new phones have the latest Wi-Fi drivers (system updates may include fixes).

Symptom: New phones may aggressively put Wi-Fi to sleep to save power.
Actions:
On the phone: Disable “Wi-Fi sleep” or “Smart battery saver” (Settings > Wi-Fi > Advanced).