For a traditional Robot voice you should likely go with a vocoder.
For the telephone effect you are speaking of, think of what a telephone does to a voice.
First matter to deal with is bandwidth. You're typically not going to get a full range of frequencies out of a cellphone, so use an EQ to limit the bandwidth to say somewhere around, 300-3000Hz. That will chop all your lows and highs and make it sound as if it's coming through a telephone.
Once the signal starts getting choppy from a low signal (meaning less connection bandwidth), that you're going to want to add clicks and pops (maybe try iZotope vinyl for this as a cheap solution) or you could vocode the EQ'd voice with some actual vinyl pops using a vocoder.
Then as it gets even worse you're going to want to use some type of Decimation/Bit-Reduction plug in to add that digital chirp and chops/drop outs until it turns into random chunks of low-bitrate static mumbling.
As cool as it may sound, using something like dBlue's Glitch plug-in won't necessarily get you what you want since a "glitching" effect is a "repeat" and that hardly ever happens on a phone. One thing that does happen is sometimes you get a echo or delay. It might be cool on something that takes place in the future or an alternate reality though. As much as I love and endorse dBlue's GLitch, it should be used in the proper context, otherwise you'll be over-designing your sound.
There are other techniques, but I tried to keep it on the cheap using only EQ, Vinyl or a Vocoder, some decimation and maybe some delay. Most of these FX except Vinyl come free with most DAW's. And I believe iZotope Vinyl is a free plug-in. Speakerphone is awesome and effective, but also a bit expensive. So if you understand the core of what you need to do, you can do it with a handful of small and cheap fx.