Coloque a validação no número da célula no angular
<div class="form-group row">
<input type="text" class="form-control" appPhoneMask placeholder="Mobile Number" autocomplete="off"
[ngClass]="{ 'is-invalid': (f.inputCountryCode.errors && mobileNumberform.submitted) }"
formControlName="inputCountryCode">
<div *ngIf="(f.inputCountryCode.invalid ) || (f.inputCountryCode.invalid && (f.inputCountryCode.dirty || f.inputCountryCode.touched))"
class="invalid-feedback">
<div *ngIf="f.inputCountryCode.errors.required">This field is required.</div>
<div *ngIf="f.inputCountryCode.errors.pattern">Invalid phone number.</div>
</div>
</div>
Poised Pygmy