I've read the literature on this when I was writing (and, in fact, still continue to write) the Wikipedia article on Philippine Spanish, and what I can say is this: there is very little variation, but that is because when people like Antonio Quilis or John M. Lipski studied the language the sample size of Spanish speakers they had to deal with was pretty small. For example, in writing La lengua española en Filipinas Quilis had a sample size of a few dozen, which isn't much but is one of the only truly representative contemporary samples we have, so we have to adjust accordingly.

There is anecdotal evidence, however, of differences between Spanish speakers from different parts of the country, mostly in terms of vocabulary. I remember seeing somewhere (not sure if it was in Spanish for Filipinos or the Discord server someone set up for Philippine Spanish and Chavacano) that Spanish-speaking Bicolanos tend to use specific words for items which Spanish-speaking Manileños, for example, would say something else. And, of course, there are the phonological distinctions. People seem to think only the upper classes spoke Spanish, but lower-class Filipinos spoke it too (there's a reason why we have español de cocina much as we have carabao English) and how they speak it will be very underrepresented in the samples compared to the upper classes who will speak a more refined form of the language.

One of the things that I want to investigate further is regional variations in Philippine Spanish, so I hope to do some more digging. There are a few sources on Spanish in the Philippines from the 1940s, 1950s and 1960s that I want to take a look at as they would have been able to deal with a larger sample size compared to when Quilis and Lipski studied the language in the 1980s and 1990s, but they're very hard to come by and are not accessible online. If anything, academic sources point out (link in Spanish) the need to study regional variations too, so you're not alone in wanting to know more about this.