Because you want to use your smartphone. Smartphones are a horrible investment and you really shouldn't buy one if you're planning on storing it in the basement in its original packaging.
Because today (and every day between now and next year) you can use that smartphone to do things that you can't do without a smartphone. So yes, the smartphone has lost money value, but you as a person and in your life, have gained.
Unless, you know, you actually want bitcoin. Maybe you want to buy something now with bitcoin (especially something that's more difficult to buy with government currency, like online gambling or illegal drugs), or maybe you just think bitcoin is cool.
Deflation would refer to the value of the same good. Obviously new smartphones are pitched as "new, improved" goods, and marketing sways consumers to get the latest and greatest.
