I think there may be confusion with the terminology. From your link and the Phonak site manuals:
The TV Connector supports Dolby Audio™, stereo or mono audio signals. Please make sure that the TV or audio source is not using the DTS audio setting. If this audio signal is present, the LED indicator on the TV Connector will be blinking red. Please change the audio signal to Dolby Audio™ or stereo (PCM) in the audio settings menu of your TV or audio source.
Note that Dolby Digital is not specified; that omission is significant. Dolby Audio is simply the blanket term for the various Dolby technologies. The Phonak device is limited to PCM digital stereo, where by comparison to Dolby Digital (or DTS), the “sound does not include discrete audio information for multiple channels. Instead, sound is extrapolated from a two-channel (stereo) signal.”
The distinction is shown more explicitly here in the Resound TV device spec:
*Stereo PCM
*- Sample rate: Up to 192 kHz
*- Sample resolution: Up to 32 bit
*Dolby Digital
*- Channels: Max 5.1
*- Bitrate: 32 kbs to 640 kbs
*- Sample rate: 32, 44.1, and 48 kHz
The Oticon and Signia TV devices (which are the same) state it this way:
TOSLINK. Either digital stereo (PCM) or Dolby® Digital
Dolby Digital and DTS formats utilize “perceptual data reduction techniques to remove useless data in PCM signal output, thereby preserving high fidelity sound." Both are 5.1 channel; they differ in bit rates and compression technology while achieving very similar results: They both remove noise otherwise found in PCM and both enhance sound quality in a way not possible with PCM, using their own codecs.
So both Dolby Digital and DTS are superior and distinct from PCM digital stereo. If the Phonak device supported Dolby Digital it would need to explicitly state so for licensing purposes (as the competitor devices do), but it does not.