With your phobia, it is often very difficult to sit in a room knowing that there is a spider in there with you. You constantly watch it, and may even drop everything you are doing to try and keep your eyes focused on it. This can get in the way of living one's life, but you can absolutely get past the need to constantly keep your eyes on the perceived danger that spiders are for you.
Our first step is for you to decide what you are watching for. Why is it that you watch spiders? Most people assume it's just to make sure they don't get too close. However, we need to try and look a little deeper than this.
A great way of proving to yourself that spiders are actually safe, is visiting a natural history museum with a bug exhibit, or a zoo with a bug house. Visiting spiders and looking at them with a thick protective sheet of glass between you and them means you can take the time to build up, by moving closer to the display and even asking the attendants for more information about spiders, so you can find out more about them.
This can be really difficult and stressful for a lot of people, so don't be nervous or upset if it doesn't work out perfectly the first time. What is most important is that you keep trying, not matter how difficult it may be.
A great way of mustering the courage required, is trying engaging in relaxation and breathing exercises. A good relaxation technique is equal breathing – close your eyes, breath in to the count of 4-6, hold to the count of 4-6, breathe out to the count of 4-6. Doing just 5-10 minutes of this every day, when you are stressed or before bed, can have wonderful effects on your mental health.
Doing this and taking your time with it, should allow you to focus on spiders a bit more and decide what it is about them that scares you; for some it's the idea of what dangerous spiders can do to a person, for others it's just the way they look. Take a note of this and keep it close by.
Something that could help you change your outlook on spiders, and therefore fear them less, is to try and educate yourself on the good things that spiders do, like keeping local insect populations down. Think of them as tiny crime fighters!