Assuming you meant that to be an "å", it's because the "to" in the English sentence is a preposition and not an infinitive mark.
There is also a world of difference between "(å) høre" and "(å) hore", so this is one of those cases where it really is worth going the extra mile and using those Norwegian characters. If you cannot access them on the device you're using, you can transcribe them like this in the sentence discussions:
æ = ae
ø = oe
å = aa
It's like the difference between "hear the radio" and "listen to the radio" in English.
"Hører" by itself is a more passive sort of listening. You're aware of the sounds -- you can hear them -- but you're not really paying attention to them.
"Lytter til" or "hører på" are more focused, attentive listening.
Edit: Nine months later, I realise I didn’t actually answer the question…. Basically, you can use either “høre på” or “lytte til”. But not “lytte på” or “hører til”. It’s just how it is!