Can I top up my phone?
ri-CA-ri-ca — four syllables with stress on the second; do not merge it into two syllables.
Use this when you need to add credit to a prepaid (prepagato) Italian SIM card. Virtually all tabaccherie offer this service for the main Italian operators.
'Posso' is the first-person singular of 'potere' (can/may). 'Fare una ricarica' is the standard idiom — you literally 'make a top-up'. The service is available for TIM, Vodafone, WindTre, Iliad, and others. You typically provide your phone number.
Vorrei ricaricare il mio TIM con dieci euro.
I'd like to top up my TIM with ten euros.
Specifying operator and amount in one sentence
Può fare una ricarica Vodafone da venti euro?
Can you do a twenty-euro Vodafone top-up?
Formal 'può' — useful when addressing an older shopkeeper
Ho bisogno di una ricarica urgente.
I need an urgent top-up.
Signals you're about to run out of credit — creates sympathy
Italy has a very high prepaid SIM penetration. The tabaccheria is the most-used point of sale for top-ups, especially for tourists who buy a local SIM on arrival. Staff are experienced at handling foreign phone numbers.