Update phone field handling in payment processing to not be passed as…

… empty string and set to 'auto'

client/blocks/upe/upe-deferred-intent-creation/payment-processor.js

@@ -34,7 +34,9 @@ const getStripeElementOptions = () => {
 			billingDetails: {
 				name: 'never',
 				email: 'never',
-				phone: 'never',
+				// The phone field is optional, so it needs to be "auto" to not throw errors
+				// when passing the phone parameter to create a payment method.
+				phone: 'auto',
 				address: {
 					country: 'never',
 					line1: 'never',
@@ -194,7 +196,7 @@ const PaymentProcessor = ( {
 								billing_details: {
 									name: `${ billingAddress.first_name } ${ billingAddress.last_name }`.trim(),
 									email: billingAddress.email,
-									phone: billingAddress.phone,
+									phone: billingAddress.phone || null, // Phone is optional, but an empty string is not allowed by Stripe.
 									address: {
 										city: billingAddress.city,
 										country: billingAddress.country,

client/classic/upe/payment-processing.js

@@ -199,7 +199,9 @@ function createStripePaymentMethod(
 					  ).trim()
 					: undefined,
 				email: document.querySelector( '#billing_email' )?.value,
-				phone: document.querySelector( '#billing_phone' )?.value,
+				phone:
+					// Phone is optional, but an empty string is not allowed by Stripe.
+					document.querySelector( '#billing_phone' )?.value || null,
 				address: {
 					city: document.querySelector( '#billing_city' )?.value,
 					country: document.querySelector( '#billing_country' )

client/stripe-utils/utils.js

@@ -385,9 +385,9 @@ export const getHiddenBillingFields = ( enabledBillingFields ) => {
 		email: enabledBillingFields.includes( 'billing_email' )
 			? 'never'
 			: 'auto',
-		phone: enabledBillingFields.includes( 'billing_phone' )
-			? 'never'
-			: 'auto',
+		// The phone field is optional, so it needs to be "auto" to not throw errors
+		// when passing the phone parameter to create a payment method.
+		phone: 'auto',
 		address: {
 			country: enabledBillingFields.includes( 'billing_country' )
 				? 'never'