if something needed to enter the cell and couldn't go through the phospholipid bilayer, how else could it enter the cell?

Through facilitated diffusion

Explanation:

A molecule that finds it difficult to enter through the cell membrane's phospholipid bilyaer can be assisted in doing so through a process known as facilitated diffusion.

Ordinary diffusion will not permit the movement of molecules against a concentration gradient or molecules can be prevented from passing the phospholipid bilayer due to their sizes/charges. Within the phospholipid bilayer exists special passages lined with carrier or channel proteins.

These proteins facilitate some molecules that will ordinarily not pass through the bilayer to pass through their special passages. This process is referred to as facilitated diffusion.