The steps are:

• Tap Settings.

• Tap Network and Internet (or Connections)

• Tap Call (or Cellular Networks, Mobile Network, or Mobile Data)

• Tap Preferred Network Type (or Network Mode)

• Select LTE and 5G (if your data plan includes 5G) and enable VoLTE / HD (High-Definition) Voice / Enhanced Calling.

OR

• Go to the dial pad of your phone.

• Tap the three dots/menu in the top right.

• Tap Call Settings.

• Tap to enable VoLTE / HD Voice / Enhanced calling.