Eggs purchased in the Cash Shop are all random reinforced mercenary eggs, you must scan them in order to randomly get phase 3 4 or 5 reinforced eggs. To get a reinforced phase 3 or 4 to an upper phase, you'll need "mid-class datas".
There is also a second type of eggs in Cash Shop: the mystery mercenary Digi-eggs: for less than 30silks, you'll get an egg to scan; It can be a random digimon among all the known types (except event limited digimon) and will be called "100% Phase 3 Digiegg". It means like a phase 3 reinforced egg, it won't break up to phase3. But you can also try to raise it to phase 4 or 5 with low class datas (it can bust then).