Sometimes phone numbers that are on emails and websites show up for a second or two and then are removed. This doens't happen with the same email or website when I use Internet Explorer
On some emails and websites phone numbers appear for a second or two and then disappear. If I reload the email or website, the number again appears for a second or two and then disappears. This doesn't happen when I open that same email or website in Internet Explorer.
Opaite Mbohovái (1)
Do you have Skype installed, I have seen similar reports about Skype causing this. Skype include a "number highlighting" option, and it may be malfunctioning and hiding the numbers instead of highlighting them. If you have Skype, try turning this feature off - http://blog.calcoastwebdesign.com/2008/11/how-to-disable-number-highlighting.html
If that does not help, try the procedure in the troubleshooting extensions and themes article, this is likely to be caused by an extension/theme issue.