Archibald Tarquin Blenkinsopp wrote
David wrote

I would like to be able to measure the ambient
temperature without carrying a bulky device.

Why? What would you want real time data on a phone as it was being
carried?

I need one for my still. You keep distilling until there is a significant
rise in the temperature, that occurs when the bulk of the ethanol has
been distilled off and you are starting to get the higher alcohols that
you don't want coming off.

Also handy with fridges and freezers to alarm
when the temp is higher than it should be.

You cannot measure ambient temperature with a phone
mounted device, or indeed any transportable device unless you
mount it on top of your head, over a very well insulated "hat".

Temperature data loggers are very cheap, I bought quite a few that
do temperature and humidity from Ebay, they have better than the
claimed accuracy on temperatue and for a pound or two extra, a
version with a pt 100 and a metre of cable is available. The thing
has an inbuilt sensor and the pt 100 takes over when plugged in.

But arent as useful when you need an alarm function.