Do I need to spoof my phone number? Or can I call from my cellphone which is different than the number that is on my stealth account?
You can call from any phone the main thing is not from the one on which you have registered a primary account.
I would advise you to call from the phone to which the stealth account is registered. If support sees inconsistencies, they can ask you for proof. But there will be typical questions to which you have answers.