Why is she suddenly acting like this around me?

There's this girl I like at work who has an outgoing personality and will talk with everyone, but with me she'll be quiet to the point we can be in the same room and not speak a word.

She'll speak in a soft tone and sometimes will sound a little nervous, she'll make glances to me (sometimes smile quickly) and turn away quick. We have flirted (she's poked me when we have) and I have complimented her, she reacts very well to this.

However, I've noticed there's this guy who hovers around her, she seems to hover around him too. She's really talkative around him, laughs and flirts. They seem to go out for cigarette breaks at work, but I noticed the other day she quickly brushed her hair before going out to have one, which sort of confirmed to me she might like him instead.

The problem is I feel jealous of them around each other to the point I've been acting distant towards her. I think she may have noticed, as she seems to make more of an effort to flirt with him when I'm around.

Today, she had been making the odd glance with a smile and I didn't react to it. When we were near each other, a good looking customer asked me for advice and we shared a joke, laughed, etc. Shortly after this other girl seemed like she was annoyed and got a bit angry with a customer for opening a box.

Later, when I checked my phone as she was talking to me, I acted distant and sarcastically and walked off. My friend then told me that this girl told him, to tell me that she was pissed off how much I was on my phone lately.

When I went up to the room she was sat in to drop off some papers, she said "Thank you" in a really soft and shaky voice, she didn't even seem pissed off with me. But later on when she wanted our managers number, my friend joked that I text her and I jokingly said "oi thats supposed to be a secret". This other girls tone then weirdly changed like she was annoyed and ordered us to stop standing around etc.

Hahaha, she is the same as I was. :) I was working in a company where are mostly men. And when i went for a smoke, I never went with a guy i liked. (I just posted about my situation) I was always ignoring this guy, but I really liked him. i went for a cigarette with my couleges, guys i liked as a company. and then this guy i liked and that was flirting with me asked me when he'll have the honor to use his break with me. so, since we worked for a phone operator, i told him intern joke like "you're on my waiting list". and there we started to communicate more, and went on breaks together.

Maybe you should go with them. Not literally, just in a same time. And start some small talk, and then you'll see. "Same time tommorrow?" will be good break trought.