I don't know whether my fear of spiders would be classed as a phobia, but I certainly have a fear of them1. However, the fear has evolved somewhat over time.
When I first moved into a place of my own, I was comfortable with small spiders, no bigger than about 5mm. I soon encountered some that were about 1cm in diameter (body and legs). I had to get someone to help me and most of them were removed. However, one lived behind the toilet and only came out of hiding when I was by myself, so I got used to it.
The following year, all the spiders I encountered were about 2cm in diameter (body and legs) so I had to get someone to help me and most of them were removed. However, a couple appeared in the middle of the room late at night when I was by myself. I managed to put them in a plastic 'spider catcher' and took them outside, so I got used to that size.
The following year, all the spiders I encountered were about 3cm in diameter (body and legs) so I had to get someone to help me and most of them were removed. However, a couple appeared in the middle of the room late at night when I was by myself. I managed to hoover them up, then empty the hoover bin outside, so I got used to that size.
Fast-forwarding to this year, I read in the newspaper that the warm spring was good for spider growth, so I waited with trepidation for the autumn when the creatures would be running around looking for mates. I wasn't disappointed – they were about 10cm in diameter (body and legs) so they scared me spectacularly. Someone helped me on two occasions, and I was most grateful, but then late at night when I was by myself another one appeared. I turned the lights down low, so that I could just about see it but couldn't clearly see its shape, then I chased after it with the hoover. I managed to corner it so it was sucked up quickly, and I was safe.
Yet another one appeared a couple of weeks later. This time I didn't panic at first, as I had a plan for what to do. It sat in the middle of the floor and didn't mind me going past to grab the hoover, so I was confident of a quick resolution. However, when I presented it with the hoover hose, it managed to avoid the air flow and ran under the computer table, startling me spectacularly. Somehow I managed to stop my hands shaking for just long enough to get it (while shouting 'Get it, get it, get it') when it wandered close to the front of the computer table, and then I shook some more once the mission had been accomplished. It took me a while to wind down after that, but at least I was safe. I can't say I'm used to that size, but I can be proud of tackling them, and just have to hope that the mathematical series doesn't continue to progress at the same rate... [touches wood, etc, etc...]