I think Phred 2 is P=0.63

https://www.google.com/search?q=10+%5E+(-2%2F10)&oq=10+%5E+(-2%2F10)&aqs=chrome..69i57j0j69i64l2.7131j0j7&sourceid=chrome&espv=210&es_sm=119&ie=UTF-8)