Buenas
tardes,
tengo
una
reservación
que
hice
por
internet.
BWEH-nahs TAHR-dehs TEHN-goh OO-nah reh-sehr-bah-see-OHN keh EE-seh pohr een-tehr-NEHT
Good afternoon, I have a reservation that I made online.
"Reservación" is used in Latin America; in Spain you'll hear "reserva" more often.