The other comments already explained it. I just wanted to add that we use <> to notate writing, so <þ> is the letter þ, not the sound. /þ/ and [þ] are the phone

The other comments already explained it. I just wanted to add that we use <> to notate writing, so <þ> is the letter þ, not the sound. /þ/ and [þ] are the phoneme and the sound þ respectively (I don't want to go into details about the difference).