The device she was using could well have been one of these.
Siemens Hearing Instruments - Our History 'Siemens patent for a compact, pocket sized carbon microphone/amplifier device suitable for pocket instruments.' ...patented in 1924.
...looks familiar.
As for who she was talking to. I would say either the guy walking in front of her or the zebra with the saddle.
If it was a time travelled mobile phone, she would definitely be talking to herself, there been no mobile networks in 1928.