I have a Uniden cordless phone #D2CT 6.0--I love the phone but the party on the other end of the line can barely hear me -how can I fix this or this a bad phone???

At 20 ft line of sight, you should have perfect reception with most any cordless phone.

The fuzzy signal can indicate:
1.
A weak signal between base and handset.
20 ft line of sight should have a good strong signal.
Your handset may be defective.
Or, your handset battery may be weak.
Your base unit may be defective.

2.
You may be experiencing RFI Interference.
Is the base unit next to any other electronic devices?
If it is next to a wireless router or some other wireless device, it may be overloaded by the nearby signal (even if on a different frequency)

I've got a 5 year old Panasonic 5.8 Ghz cordless phone connected to my VoIP box. I just tested it from about 25 ft away from the base unit in another room with a wall in between and my reception is perfect.

I did the same test with my Panasonic DECT 6.0 phones (1.9 GHz). The first handset is slightly fuzzy, but otherwise good signal. The 2nd handset was perfectly quiet with good strong signal. So, there is a difference between two identical handsets connected to the same base unit. This indicates to me that one handset is better tuned than the other. Nothing I can do about that but get a new 2nd extension cordless handset. Sometimes, it's just luck of the draw