Pham hit .226 in 2016 and didn't have a very good spring last year, either (.209 BA). He had shown flashes of promise, but he was not a proven MLB player one year ago, so it wasn't really surprising that he started the season in the minors. Matt Adams was clearly more highly regarded offensively, so the Cardinals tried him (unsuccessfully) in the outfield.
He should be ecstatic that he put everything together last year and had a great season, rather than worrying that he didn't get called up a week earlier than he did.
Pham had a 140 wRC+ after coming back in June through the middle of August in 2016 before going 0fer in a few games and getting benched for Grichuk and Brandon Moss, who are much worse hitters than a fully healthy Tommy Pham. Now, he did supposedly have eye issues, but he was very good up until a week of 0 for 15 or so and then got sporadic playing time for the rest of 2016. Cardinals missed the playoffs by 1 game in 2016, and Tommy probably felt he was the difference if he got to play (maybe justifiably).
Matt Adams is maybe slightly better than league average hitter and probably the worst defender in LF of all time if he were to get a full season out there. And it wasn't the Cardinals brass putting him out there, Mozeliak had to trade him because I highly doubt anyone but Matheny wanted to see that nonsense continue. Having him play the outfield while Tommy Pham wasted 100 plate attempts in AAA in 2017 had to be an insult. The Cardinals missed the playoffs by 4 games last year and Tommy thinks he would have been the difference (definitely justifiably).
Tommy Pham is probably a hard guy to get along with (most intensely focused professional athletes probably are), but he's not wrong about anything he said in that story. And if he goes out and puts up another 4 or 5 win season, the Cardinals will likely make the playoffs.