How do I delete printer from iPhone?

What do you mean it defaults to your printer instead of your Wi-Fi? Are you trying to connect your phone to the printer or the Wi-Fi? Your statement does not make sense. The only time the iPhone sees the printer is if you are trying to print and the phone is connected to the same Wi-Fi. Trying to connect the phone to Wi-Fi should have no bearing on the printer or vice versa.

It appears that you have your printer set up to broadcast Wi-Fi. You need to configure that on the printer. The only way that your phone would see the printer in the Wi-Fi settings is if it is broadcasting its own Wi-Fi. Check the manual for the printer and turn off Wi-Fi broadcasting. If you need it to be broadcasting, then when you are connected to the printer via Wi-Fi in Settings, then tap on the ℹ next to the printer name and click on Forget this Network. That should remove the network from the phone and do the same on the iPad.

Forget this network should do it, but I've not experienced a printer listed as a Wi-Fi source. Good luck.