My voice to text is not working. How can I fix it? I have an iPhone 5. Thx!

On my iPhone 5c, voice to text does not work in any program, notes or text or phone. Voice memos can hear my voice but not Siri. How much disc space needs to be available? Is that a factor? Less than a gig available on my 8gig 5C provided by work

Define "not working".

Siri must be enabled for this feature to work.

Hav you tried backing up and reseting all the settings?

Turn off your Bluetooth and try again