One of my favourites!
I had seen some site where they did give the phonetics.
Have you tried googling it?
What you should do is find a basic guide to the Welsh language, like the one at BBC Wales for example.
It's an incredibly difficult and subtle language and you wont get the phonetics right in day, so it's worth studying.
Anyway, here's a stab at it but I'll be glad to be corrected:

Dah-koo nyaw-rree-ahd ee lawrr un uh berrfthlan, too rrumdi rrahdl eedl awl.
O nah baoon ee uhnoh vuh (or vee?) heenawn, too rrumdi rrahdl eedl awl.
dah-koo'rr tuh, ah daw-koo'rr 'ssgeebor; dah-koo dth-rrooss uh bay-eeduh'n ahgohr.
Fawldee rrahdl eedl awl, Fawldee rrahdl eedl awl, too rrumdi rroh rrumdi rrahdl eedl awl.
Dah-koo'rr dtherr-ouen oueekh gahnghehnohg, gohloog ahrrnee ssuhdth varr ssehrrkhohg.
Mee ahrrhossav uhn eye khussgohd nehss daoo nyaw-rree-ahd ee nguhvahrvohd.
Dah-koo'rr deluhn, dah-koo'rr tah-nah-ee; beth ooeev goo-eh-fthl, hehb nehb ee'oo khouarrai?
Dah-koo'rr vInooehn heyneess vahnool; beth ooeev nehss hehb gail eye mehdthool?