"Hello. I'd like to make a reservation, please. For Monday night at 7:00pm. For 2 people." They may ask, "How many people in your party?" This does not mean "party" like a festa or birthday party. I just means "group". You can say, "It's a party of three", for example.

Pode falar assim: I would like to make a reservation for ( numero de pessoas ) on ( data mm/dd/aa ) at ( hora ). ou também: I would like to book a table for tonight, for 6 people at ten o'clock.