Indian citizens needs an invitation letter to apply for a visa for Philippines. Can this invitation letter be issued by an individual? More so what is the format of such an invitation letter?
Yes, it can come from either a business or an individual.
Several nationalities require an invitation for the Philippines. It's common, and other countries (Uzbekistan, Russia) often ask for it too.
If you don't know someone there, there are often companies that will send you an invitation for a fee (crazy, but common).
However, if you do know someone and want to know what it should have, the requirements for the visa for Indian citizens state:
A letter of invitation from sponsor (either host company or individual) explaining the relationship to the applicant and the purpose of travel. In addition, the letter must indicate the length of stay, place of stay, and contact information.
Hope that helps!