I'm a foreigner. Can you speak slowly?
'Straniero' — 'stra-NYE-ro'. Three syllables; 'ie' is a diphthong.
Use at the beginning of the journey if the driver speaks quickly or uses dialect, to establish that you need simpler, slower Italian.
'Sono straniero/a' (I am a foreigner) immediately explains the communication need. 'Può parlare lentamente' asks for slower speech. Most Italian taxi drivers will switch to clearer Italian when they understand the situation.
Parla inglese?
Do you speak English?
Direct question; many urban taxi drivers have basic English.
Sto imparando l'italiano.
I'm learning Italian.
A charming opener that often prompts encouragement from the driver.
Non ho capito. Può ripetere?
I didn't understand. Can you repeat?
Use during the journey when something is unclear.
Italian taxi drivers are often chatty and curious about foreign passengers. Admitting you are learning Italian is usually met with warmth and patience. Many will switch to simple tourist-friendly Italian to help you practice.