Hi Liza.
To prove that he has the intention to return to the Philippines, your friend needs to provide evidence which include but shall not be limited to the following documents:
1. Employment Certificate
2. 6 months pay slip
3. 6 months bank statement
4. Records of savings
5. Records of Assets (i.e. house, lot, business, etc)
OTHERS
6. School records (if student)
7. Marriage certificate (if married)
Hope this helps.