I've validated it myself for an argument when the comic was published for the phrase "correct horse battery staple".

First character is 4 bits: c = 4

The next 7 chars are 2 bits/each: "orrect " = 14

Characters 9-20 are 1.5 bit/each: "horse batter" = 18

Charactes 21-n are 1 bit/each: "y staple" = 8

No bonus for including both upper and non-alpha chars.

No bonus for passwords of length less than 20 chars, not containing dictionary words, because the password is longer than 20 characters.

Total entropy: 4 + 14 + 18 + 8 = 44 bits of entropy.