The applicant and the insured have a guardianship relationship. If the insured is underage, the applicant may sign on his behalf. It doesn't matter how you call back, even if the other party records it, you can't deny the insurance contract that should be valid.

If the insured is an adult, the insurance contract must be approved and signed by the insured before it becomes effective. If it is signed on behalf of the insured, the insurance company will check the signature when the insurance liability occurs. If the signature is invalid, it can refuse to pay compensation.

In the second case, before the insured accident happens, just let the insured sign for confirmation.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.