Low spatial frequency means not much information is present, so you have to do extra work to make out what you are looking at. Iain McGilchrist, The Matter with Things, Chp. 2.
Looked at through Marshall McLuhan lingo:
“Hot” media and “cool” media were McLuhan’s buzz dichotomy. A hot medium is "high definition." It provides lots of content to one of the senses. The radio is a hot medium: ear only, and a lot of it. It's one of high spatial frequency.
The telephone, on the other hand, is an extremely cool medium [one of low spatial frequency]. The ear doesn’t receive much information, forcing the user to participate, to fill in the gaps.
[W]hen the signal is easy to read, the left hemisphere is slightly quicker at detection (it tends, compared to the right, to jump to conclusions), but when the signal is any way degraded, partial or hard to read, the right hemisphere is more accurate. McGilchrist, Id.
So it seems the right hemisphere is probably more engaged when it comes to the telephone.
Is the result that the master of our psyche (the right hemisphere) is thereby preoccupied, making it hard for us to do other things when we're talking on the phone?
I think McGilchrist would agree. After spending a lot of time exploring the effects of brain damage on the ability of patients to perceive with their five senses, he states this about LSD:
I am sometimes asked whether the experiences of people taking hallucinogenic drugs are due to right hemisphere ‘release’. I am very doubtful of this. There is very little direct evidence, but on first principles, it seems more likely that, to the extent that lateralisation is a significant factor, they are caused by suppression of the right hemisphere. . . .
This implies that hallucinations are more often due to right hemisphere than left hemisphere dysfunction. . . .
Almost all extraordinary distortions of reality follow from right hemisphere damage. . . .
Shortly later, he offers this summary about the hemispheres and the senses:
In every sensory modality the right hemisphere appears to have an advantage over the left when it comes to primary perception. Perceptual distortions and hallucinations in each sensory modality are strongly associated with right hemisphere dysfunction. Thus, as far as both attention and perception go, the right hemisphere is a more important guide and a more reliable one to the nature of reality.
Does that mean the left hemisphere is better at multi-tasking, which would make sense because the left hemisphere is obsessed with efficiency and multi-tasking is nothing less than the pursuit of efficiency? If it's the part of our brain that is engaged, we can still function in other ways.