For security reasons, there is a restriction on the number of times you can attempt to login using your phone number in quick succession.
If you see the error message 'We're having a problem logging you in. Please try again later.' - this means that you have attempted to login too many times. Please try again several hours later. We find that you can make a further attempt approx 5 to 6 hours later.
This restriction is a security measure and is imposed by our 3rd party authentication supplier. Unfortunately they don't disclose how many attempts you can make or what the timeframe is as it can change.