You need to fully assess your client's tax residency in IL.

Is IL your client's state of domicile?

Did the spouse and dependent(s), if any, relocate with your client?

For what purpose did your client relocate to the Philippines?

What is the intention and realistic expectation of the duration of residency in the Philippines?

What facts and documentation does your client have to support the intention and realistic expectation?

What actions have your client taken to severe social and economic ties with Illinois and establish the same in the Philippines?

These are some of the questions you should always ask your clients.  Illinois' rulings on foreign assignments are not the most favorable to domicile residents who are on foreign assignment/employment despite the presumptive rules in the regulations.  Luckily, IL does allow foreign earned income exclusion (although foreign taxes are not creditable).