Create exposed filter for Views PHP value
If you are using Views PHP, then you are using it's alpha or development version. Alpha tests means that maintainer expects there to be bugs and want you to report them in issue queue. Development version almost certainly have issues, that's the nature of ongoing development.

Having that said, you shouldn't attempt to use exposed filters on fields that are not in database, and cannot be readily joined and used in SQL WHERE with your data. Unless, of course, module that provides it already implemented it properly, and it appears it is not the case here. So your options are:


Forget Views PHP for dates, and use regular Date to get date fields attached to your entities, and Date views submodule for views exposed filters, or
Post a bugreport and wait for it to be fixed. Just don't really expect it to happen, as module currently lacks manpower and is seeking co-maintainers.