Both Alita and Dark Phoenix were scheduled to hit theaters this year at different points in time, but had already been delayed once prior to today's news. Gambit, on the other hand, has been pushed back several times by this point and still has Channing Tatum (loosely) attached to star as the Ragin' Cajun, but is currently without a director.
As of today, Fox has officially moved Alita from December 21, 2018 to Dark Phoenix's most recent launch date on February 14, 2019. Dark Phoenix will instead open in theaters four months later on June 7, with Gambit now delayed until March 13, 2020. However, perhaps the most surprising Fox-related news of the day is that Alita's old spot has been filled by a PG-13 theatrical cut of the sequel Deadpool 2.
Dark Phoenix's release date delay comes as something of a shock, seeing as the first Dark Phoenix trailer was only just released this week. The film (which was directed by longtime X-Men writer Simon Kinberg) had previously been pushed back from its original November 2018 release date, in order to allow time for its reshoots to be completed this past summer. As its stands, Dark Phoenix will now open against Illumination's animated sequel The Secret Life of Pets 2 at the box office.
Alita's delay, on the other hand, comes as less of a surprise. Filmmaker Robert Rodriguez's live-action anime/manga adaptation was originally set to hit theaters back in July, before it was delayed to mid-December this year. The film hasn't been generating a lot of buzz and would've had to compete with several other tentpoles on its December date (including, Aquaman and Bumblebee), so its chances of box office success have now improved significantly thanks to this delay.
As for Gambit - Kinberg recently confirmed that the X-Men project is still moving forward and described the movie as having a romantic comedy vibe in its current form. The spinoff has been delayed so many times by now that it's difficult to say whether things will work out any differently this time around, even with its release date pushed back another year. Moreover, by that point, Disney will (barring any last-minute unforeseen obstacles) have formalized its purchase of Fox and, thus, be able to make the X-Men official members of the Marvel Cinematic Universe - so who knows how that will (or will not) impact Tatum's Gambit spinoff.
Source: 20th Century Fox