To change phone number into optional follow the below configuration setup

Go to Admin Login -> Stores -> Configuration -> Customers(Tab) -> Customer Configuration -> Name and Address Options.

In their change Show Telephone is Required into Optional.

Now the checkout page is not asking the Phone number is required.

To change phone number into optional follow the below configuration setup

Go to Admin Login -> Stores -> (Settings) Configuration -> Customers(Tab) -> Customer Configuration -> Name and Address Options.

In their change Show Telephone is Required into Optional.

Now the checkout page is not asking the Phone number is required.