still i couldn't send message from UK to the philippines. I'm using iphone6. does iOS has something to do with it since iphone6 can only update up to 12.5.6

Send a message??

Imessage or SMS is independant of iOS version. If the recipient is not an iPhone user you need to know if your neytwork provider and their network provider allow international SMS texting

If they are an iphone user then both of you could do this

Settings, Messages, Turn off iMessage

Settings, Face Time, Turn off Face Time

Restart the phone.

Settings, Messages, Turn on iMessage, SMS, MMS

Settings, Messages, send & Receive, select your number which should now be there.

Settings, Face Time, Turn on Face Time