For EMS, UPS, DHL, and Fedex, you are required to input a phone number.
(an error will occur if the phone number field is left blank).
In Shopify, when the purchaser inputs their information, there is an option to make entering the phone number mandatory.
For details, please see the following.
Settings → Check out → Form Options → Delivery Phone Number → “Make Mandatory” (select “Make Mandatory”).
If you make these settings, there is no need to worry about an error appearing if the phone number field is left blank.
Please see Shopify’s website for more detail: https://help.shopify.com/en/manual/sell-online/checkout-settings/checkout-form-options