UK area code
Fordingbridge area code
Fordingbridge is covered by 01425 and 01725. It sits across a boundary between dialling areas, so which one applies depends on which part of Fordingbridge you mean.
01425The Ringwood dialling areaSee what 01425 covers →01725The Rockbourne dialling areaSee what 01725 covers →
If you have the number already, the code it starts with is the answer — that's more reliable than the town name for a place split like this. Look it up.