I believe symbolic here means that it won't actually function to deter illegal immigration, at least not proportionally to spending that money on other efforts.

Is Israel's border wall symbolic or physical?

I am not sure what your point is. A thing can be both symbolic and physical. Let me know what you want me to clarify. I thought I was pretty clear in the above comment.

Physical things can be symbolic...

A wall symbolizing keeping out foreigners without actually doing anything useful to do so is pretty much the definition of symbolic.

yes, I meant that the wall will physically exist but it's more of a symbol - a KEEP OUT sign of sorts - than an effective tool for border security... or at least not a cost-effective tool.