Should I still apply for a phd if the PI can't confirm if he is able to fund?
If the cost and time are reasonable by your standards the I'd suggest you do it for the experience if nothing else. There is little else to lose in this. 

Applying isn't a commitment on your part, it is just an expression of interest. Even in the worst case the professor will probably continue to have good feelings towards you, which can help in the future if you work in related areas. 

But there is no reason to wait for a decision. You can explore other opportunities in parallel with this. Decline only when you must.