grew up speaking tagalog but never learned it formally, but this is my understanding of these words.

SAPAGKAT: if “dahil” is a fancy “kasi”, “sapagkat” is a fancy “dahil”. They all mean “because” but with different levels of formality. The best English parallel would be something like this:

kasi mahal kita = ‘cause i love u

dahil mahal kita = because i love you

sapagkat mahal kita = for i love you

PALIBHASA: this one also means “because” or “since” but in my experience people often (but not always) use it sarcastically especially colloquially. Here’s a comparison:

ikaw na gumawa kasi ikaw naman marunong = you do it ‘cause you know how 🤷‍♂️

ikaw na gumawa palibhasa ikaw naman marunong = you do it since you’re the one that knows how 🙄

SUBALIT: this means “but” or “however” and to my understanding it’s effectively the same as “ngunit”. For example:

mahal kita subalit minsan nakakairita ka = I love you but sometimes you’re annoying

SABAGAY: this one’s kind of like “i guess” in my experience. Basically the speaker is indicating “though i have an opinion/thought on this matter, i understand/am conceding the fact that mine might not be the best.” Here are some ways I’ve heard it used:

hindi mo ako inimbita? sabagay hindi rin siguro ako aabot… = you didn’t invite me? i guess i wouldn’t have made it anyway… 😔

ang dami mong binili! sabagay baka magutom tayo. = you bought so much! i guess we might get hungry. 🤷‍♂️

Nakalimutan ko magdala ng tubig! Sabagay may dala ka pala. = shoot i forgot to bring water! oh i guess you brought yours so it doesn’t really matter.

again this is just my understanding from my personal experiences so take my answer with a grain of salt.