Numbers from 0 to 9 are
0  zero
1  um
2  dois
3  três
4  quatro
5  cinco
6  seis
7  sete
8  oito 
9  nove

When reading phone numbers it is common to say meia instead of seis. Meia means half, in this context meaning half a dozen. It is used because it is easy to mix seis with três. (Obrigado Glaucia)