[Python] Computing Eulers Totient Function

I am trying to find an efficient way to compute Euler's totient function.

What is wrong with this code? It doesn't seem to be working.

def isPrime(a):
return not ( a < 2 or any(a % i == 0 for i in range(2, int(a ** 0.5) + 1)))

def phi(n):
y = 1
for i in range(2,n+1):
if isPrime(i) is True and n % i == 0 is True:
y = y * (1 - 1/i)
else:
continue
return int(y)

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