First of all, I can assure you that most Filippino people - especially in Luzon - speak and understand English very well. Their English has usually some filippino accent ... but its is clear and the extent of their vocabulary is sometimes amazing.
I suppose you are not a native English speaker ... just as me ... I am no native English speaker as well. I have travelled a lot in the phils and people did understand me almost always with no problems at all ... so there must be another reason why they dont understand you. And only you can really know, what might be the reason for that ... so I will refrain from speculating about it.
As @jkos has mentioned: if you have problems to communicate in English, it might be a good idea to learn some Tagalog ... which is widely spoken in Luzon ... but that will probably take some time an effort ... And it may not always work if you travel to other islands than Luzon ... as some people do not speak or like to speak Tagalog, especially in rural areas ... Visaya, Waray, Cebuano ... just to mention a few ... ! Or people have strong accents ... like in Mindano, where they tend to change vowels a lot (eg. aku instead of ako )
So I hope you will get along well in the phils ... people are reallly friendly and helpful and they will try to understand you, if you just give them a chance to do so ...