A:Answer You asked ...
FICO is a meaure of credit worthiness. The way it is accessed...
1. How much open debit you have
2.Late payments, delinquency, bad debits
3. Your debit ratio , credit utilization in other words with open credit do you have more than 30% used. For example, you have a credit card with a limit of $3000, 30% of that would be $1000 , now if you have used more that $1000 , that drops down your FICO further.
A low FICO does not always signifying a negative picture, it could reflect a person has very little open credit and prefers paying in cash. A person with a FICO of 800s tells me they have $10000s in debit that they are great at paying off which is exactly what big business loves.
Debit is not your friend.
Not knowing your financial picture I cannot tell if getting a phone will help or harm you but getting into debit to improve your FICO is not the wisest move to make.
What happens next year when a new iPhone comes out? Guaranteed it will be an even better phone and you could be in a stronger financial position, if you decided to hold off and make some financial changes.
Good luck with your decision, I hope this was educational ( no judgement)