Basic English phonics is easy to learn and teach. Most (41) of its 44 sounds can be shown in simple words: a (at), ai (aim), air (hair), ar (art), au (autumn), b (bed), c (cat), ch (chest), d (dad), e (egg), er (ermine), ee (eel), f (fish), g (girl), h (hat), i (ink), ie (pie), j (jam), l (lip), m (mum), n (nose), ng (ring), o (on), oa (oak), oi (oil), oo (ooze), or (order), ou (out), p (pin), r (run), s (sun), sh (shop), t (top), u (up), u-e (use), v (van), w (with), y (yes), z (zip), si (vision) and the unstressed half-vowel of ‘father, fasten, decide’.
Short /oo/, as in ‘could, put, book’ is trickier because it has no spelling of its own, and the two sounds of ‘this thing’ are both spelt 'th'.
But that's very basic stuff and does not get you very far in learning to read and write English, because most sounds have several spellings (oo: blue, shoe, too) and many spellings have more than one pronunciation (a: an, any, able). I don't speak Welsh, but get the impression that Welsh spelling is much simpler.