I'm far from a high level speaker, so take the answer with a grain of salt: This is the result of the construction ~ㄴ 것 being applied to the verb 증가하다, to create the meaning: 'the action of something increasing' (in the past) The construction '~(으)로' carries the meaning 'through, or by using'. So the full construction: '증가한 것으로' is interpreted as 'through/because of the increase in'. I think this makes the entire sentence translate as roughly: 'A drastic increase in mobile phone shopping customers has arisen from many people becoming smartphone users'

것으로 is basically just 로 being used with another grammatical device (specifically, turning a verb into a noun). In this case, 로 is more like "as". 급격히 rapidly. sharply 증가하다 to increase, to grow 증가한 것 an increase, growth 증가한 것으로 as something that has increased 나타났다 appeared, to have appeared, to have shown The sentence translates to something like: As the number of smartphone users has gone up, the number of mobile shoppers has shown rapid growth. I highly recommend studying the grammar relating to ~ㄴ 것, ~는 것, ~ㄹ 것 if you want to understand how the grammar interacts with the words.