Substitute pops note with flyer inside ladder (8)

'substitute pops' is the definition.
(pop can mean one's father)

'flyer inside ladder' is the wordplay.
'flyer' becomes 'dad' (I can't justify this - if you can you should give a lot more credence to this answer).
'inside' means one lot of letters goes inside another.
'ladder' becomes 'steps' (I've seen this before).
'dad' going into 'steps' is 'STEPDADS'.

'note with' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.