The build seems pretty solid. I think you should go more survivability early game than attack speed.

Heres what I would do:
I would get the Ruby Crystal first to build up to the Phage, that way late game you can get the Frozen mallet.
Next get the boots of swiftness that way you can give chase or retreat if needed.
After you got your boots then start saving up for the Last Whisper, and follow the rest of the build as is.

Very interesting tho, Can't wait to try it.

Vote and tell me what you think about my build