Angular 7 Reactive forms "No value accessor for form control with unspecified name attribute"

seems you cannot have a @Input() named formControl

One little thing I see is this:

  <app-telephone-input i18n-placeholder placeholder="Other Telephone"
                       [formControl]="form.get('otherTelephone')">
  </app-telephone-input>

So it should be:

  <app-telephone-input i18n-placeholder placeholder="Other Telephone"
                       [appFormControl]="form.get('otherTelephone')">
  </app-telephone-input>

If you want to create a custom form controler you should implement ControlValueAccessor interface

ControlValueAccessor {
  writeValue(obj: any): void
  registerOnChange(fn: any): void
  registerOnTouched(fn: any): void
  ...
}

If you implement ControlValueAccessor interface only you can bind property formControl