It does seem not quite right.. There is nothing wrong with 'more and more' in formal writing. Clive.
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It doesn't seem grammatically correct, but it does have a slightly different meaning to 'more and more.' It suggest that the amount of people is growing, rather than only showing the amount.
It's a weird phrase that I know I use when speaking but in print it just doesn't sound write (native speaker).
I think it's not technically redundant (if you put a comma after "increasingly") because there are two "increasing" items:
1. A greater number of people ("more") are purchasing smartphones. In other words, more people are purchasing smartphones today than were purchasing them yesterday. "More people are purchasing smartphones" is retrospective in that it means people were purchasing fewe