Why don’t I have WiFi to back up my phone if it’s a hotspot??

Turn Hotspot Off.

Connect your iPhone to Wi-Fi network.

See the following Apple articles:

Connect to Wi-Fi on your iPhone, iPad, or iPod touch

https://support.apple.com/en-us/HT202639

See this Apple article: If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

https://support.apple.com/en-us/HT204051

Wifi is an external entity which is not directly affected by the iPhone internal hardware condition. Hotspot requires the phone to internally maintain the full 3G/4G signal that is carrier data, thus any quirks in the iPhone can break the signal. Only 5G is wide enough and stable enough to replace wifi in this role and is new on the landscape.