Are there fewer firmware chips in a mobile device compared with a laptop or a desktop?
I would go with a cautious &quot;yes&quot;, simply because the BOM is smaller - there are fewer functions, so there are fewer chips, and they're all on one board, and they don't need to be pluggable or standalone.
The place to look is teardowns such as iFixit that enumerate the chips. However, you still need to check if each package contains multiple dies, one of which may be internal Flash for more firmware.
Subsidiary chips may contain firmware in mask ROM, but since this is unchangeable it's not of security interest.