You may want to improve your ecommerce page, if you want to increase your conversions.

Your rankings are probably dropping, because:
- you have previously exchanged links
- are selling links to unrelated sites on your site
- you weren't active in getting good quality links

So first, you need to:
- stop exchanging links
- remove links to sites, unrelated to cell phones
- don't buy or sell links

To rank high, you need to get good links (think quality, not quantity). To get the good links to rank, you need to:
- know your customers
- create useful articles for them (you can try creating well researched, useful top 7-50 lists for them)
- promote them on social sites

Essentially, you can start a blog. You can read more about blogging in my recent article and also read about:
- creating content
- creating link worthy content
- improving your website usability

Cheers.