Enable or Disable Wi-Fi Calling
Wi-Fi Calling allows you to call and text via Wi-Fi and bypass using the cellular network. So, if you have a weak cell signal but a stable Wi-Fi connection, try using Wi-Fi calling if your carrier supports it.
On the contrary, if Wi-Fi calling is enabled, your iPhone may prioritize Wi-Fi over cellular. If Wi-Fi Calling is enabled and your Wi-Fi signal is weak, try disabling Wi-Fi calling.
To control Wi-Fi Calling, go to Settings > Cellular > Wi-Fi Calling and toggle the switch beside Wi-Fi Calling on This iPhone.