Well, there's certainly a balance between what % of keyword searches you can expect to capture. Lower volume words like offer less traffic but if targeted they should have better CTR - right? We know this. Using Moz tools to quickly check your site, you have good links and optimization, so there's two other things to explore: the keyword isn't as viable as you think it may be and possible technical issues with your site that impact the end user.
What does your Webmaster (or other analytics tool) show you? is that term driving traffic and/or what other keywords are sending people to your page? What's your bounce rate? If it's high and tied to your keywords, then perhaps it's not the fit you think it is. Have you considered going for a higher volume term, like 'hosted voip' and then 'business hosted voip' on a different page?
As for technical issues, that's a whole other slew of things that I am sure other Mozers can speak to in better authority than myself. From a quick look, again, you seem pretty solid here. You did a nice job getting a lot of things right - including rankings. So I'd look at other keywords to expand opportunities.
