The prime factor of 49 is 7.
φ(49)=49(1-1/7)=49×6/7=42.
This is effectively the same as counting the numbers which are not multiples of 7 between 1 and 48. More specifically those numbers not having a prime factor in common with 49 (coprimes).
So we exclude 7, 14, 21, 28, 35, 42, and 48-6=42.