Best way to get from Phi Phi to Koh Lanta and then down to Libong

In high season it's a breeze. Get the ferry between PP and Lanta - normally 2 per day. Then get the Tigerline ferry from Lanta which calls in at the Hat CHao Mai pier (aka Hat Yao pier) on the mainland near Trang - the public longtail taxi boats to Libong leave from near the pier when there are enough passengers - usually each hour.

Now in the past those ferries have not run in low season.
In that case you will need to ferry PP to Krabi, catch the minibus onto Lanta, then catch the minibus Lanta to Trang, then catch the songthaew to Hat Chao Mai.
I have details of all these transport links plus the 3 islands in the first link below.

Oh yeah, in high season there is also a Lanta Lipe speedboat which drops off/picks up at islands on the way. They may be prepared to drop you off directly at your resort on Libong. I don't have a link but any guesthouse or small travel agent on Lanta will be able to inform you, book ticket etc.

Thanks a lot Tezza. Very useful!