phone input: fix auto validation on invalid

src/lib/PhoneInput.svelte

@@ -160,7 +160,10 @@
 				{placeholder}
 				validate={{
 					required: required,
-					func: () => !required || (value !== undefined && value.isValid())
+					func: () =>
+						!required ||
+						(value !== undefined && value.isValid()) ||
+						(lastValue !== undefined && lastValue.isValid())
 				}}
 				onvalidate={(e) => {
 					numberValid = e.detail.valid;