No, it's not. Here are some old threads on the topic:

https://www.reddit.com/r/AskHistorians/comments/2mkve2/is_there_any_credibility_to_the_phantom_time/

https://www.reddit.com/r/badhistory/comments/3cho2p/im_new_has_phantom_time_already_been_discussed_if/

I read a conspiracy theory a while ago. Just curious to see how somebody would answer. Please don't bite my head off for asking.