ph [f] broad and slender
th [h] broad and slender
ch [x] broad, [ç] slender.
All these are voiceless fricative sounds. [f] and [h] will be no problem, but [x] and [ç] will be unfamiliar to English speakers. If you have a bit of German, [x] is the sound in "ach", and [ç] is the sound in "ich". [x] is the final sound in "loch". If you have trouble pronouncing it, this word will probably come out as "lock". That's because [x] and [k] are pronounced in the same spot (point of articulation). The [ç] sound is pronounced more towards the front, in the same spot as the <k> in "keep". you can listen to these sounds (and some more) at Fuaimean na Gàidhlig - Fricatives @ akerbeltz.
In order to practise [x] and [ç], you can attack them from two fronts: