There are supposed examples of witches being able to control weather. The idea gets discussed in much depth depending on the study and context of witchcraft, sometimes called neo-physics in the modern age. The idea seated behind the spell craft deals with energy manipulation. It used to be that Wiccan was synonymous with Witch, now there seems to be a great distinction depending on whom you converse with on the subject. Nowadays, Witch is most identified as someone with Wiccan or Pagan pantheonic belief systems but that in addition believe that they are able to personally manipulation energy in various forms. Weather is as all things, a manifestation of energy, revealing itself in various forms of precipitation. It would be only natural for a witch to believe they are able to control weather, if they believe they can control energy.
How she did it is another thing all together. If she is using a phone immediately prior to "controlling" the weather, and in addition asks about the speed and direction of the wind, it might just be she has an immensely organized mind in regard to being able to mentally anticipate where a storm is going to be. Sort of like those old and very annoying algebra questions in middle school. e.g., if a rain cloud leaves Denver Colorado at 5PM and travels along a wind stream pushing at 90 miles an hour, what time will it arrive in Aspen. This action of weather "control" is no different than what every pilot in existence has learned to do and perform at one point or another.
If you are looking at it from a Witchcraft point of view, there are various ways weather is controlled. Many witches usually claim to be able to effect only one particular type of weather, a specialty if you will. Water witches are some of the most common. Many witches have the best ability to make weather change usually when it’s associated with a pre-thought out feeling. Some witches are able to control rain in various intensities when either immensely sad, or violently angry. Most common associations: immensely happy, promotes a sunny day. Horribly sad, a slow, heavily overcast rain. Violently angry, anything from hail to severe thunderstorms. In the archives of history, witches believing that the craft promotes controlling energy in all its forms tend not to associate with just one emotional weather form. All weather being a manifestation of energy means they should be able to control all of it, from rain to sun or cold to hot. This type of Witch may use meditative association. That by trying to channel a specific feeling or image they believe associates with how they feel in a type of manifested weather and thinking that through induces the emotion which induces the weather.
It is believed that anyone with enough dedication would be able to control weather and there are countless examples going back hundreds of years. There are people who are not proclaimed witches that notice weather changing with their desires and emotions.
There are scientific methods which boast the ability to create weather. It’s also sometimes called weather modification. Machines built, and some still theoretical machines, are supposedly able impregnate clouds with the ability to either snow, rain or other modifications. That technique is called cloud seeding. I doubt this is something your girlfriend did with her cell phone.
In conclusion, there are countless theoretical scenarios and cased evidence. If you want to try and pinpoint your direction of discovery for this action, you need to question your girlfriend more.