Devoiced sound phenomenon in English

What is the phenomenon when some sounds are devoiced in pronunciation?

Some sounds are devoiced in the cases as the following:

The approximant [ l r j w ] will be devoiced when standing after fortis plosive [ p t k ]

plan / pl̥æn ]

between /bɪˈtw̥ɪːn /

cry / kr̥ɑɪ /

tuesday / tj̥ʊːzdeɪ/

question / kw̥ɛstʃ /