No matter what app it is, if employers require one to be used on a smartphone, they are legally obligated to provide you with a work phone. If they refuse, they are legally obligated to provide reimbursement for your personal mobile plan. This can be as simple as $5 or $10 added monthly to a paycheck, or as detailed as actual usage down to the kilobyte.
Even if it’s as simple as clocking in and out. If they won’t provide a phone or reimburse, they must have some other method to complete the task. Whether it be a computer or paper. Failing that, they are not upholding the law of providing you tools necessary to complete your job. Which means if they terminate you for any of the above under “not able to do your job”, it is retaliation for you requiring them to do their job. You could potentially win a suit against them.