Well I can't see Phil going Sikh anymore than him going Muslim, and for much the same reasons; he lacks discipline and he's scared of brown people. Sikhi might be worse because an overwhelming majority of Sikhs are Punjabi even in the diaspora. And forget about him going Amritdhari because he would be too embarrassed and scared to actually wear a turban in public!
Actually I'd say Sikhs are pretty well known and even trendy in certain internet circles these days, though that doesn't really equate to much actual knowledge of their beliefs or practices, let alone many white hipster converts. Phil tends to be ignorant and behind the times so I doubt he knows the Sikh faith even exists of course despite being one of the largest religions in the world. I suspect he's one of the ignorant masses who assumes they are Muslim or Hindu simply because they can't fathom the idea of multiple religions existing in South Asia.
On the other hand, Phil would absolutely love the idea of Khalistan and Sikh nationalism/terrorism because of course he would. Those sorts of beliefs are almost exclusively found outside of Punjab and outside of India in general these days specifically because the locals have had enough problems dealing with terrorism and ethnic separatism in the recent past. Only a gora with no connection to India would get so radicalized.
Of course, Phil's other problem is that most Desis don't care about some weird gora playing dress up, but his SJW friends would definitely accuse him of "cultural appropriation." Ironically they are as racist as the white supremacists. They don't want white people dressing, eating or worshipping as Indians!