Microsoft, for example, has how many hundreds of millions of Teams users? If anybody has the knowledge and resources to build an efficient application, it's Microsoft. But instead, to save pennies per user, they build with Electron and waste a huge amount of energy.
The big secret? Electricity costs money, and is taxed.
Basically - why fucking bother with trying to measure and assess these applications when there are already measurements on the root consumption - electric power.
Long story short - it's a pretty useless thing to be focused on - it costs well under $5 to charge a smartphone for a year's worth of usage. There are simply much, MUCH more impactful changes we could be focused on.
This is a waste of time.
Honestly - not really. Yes, it's large in the abstract sense that it's a very tiny number multiplied by a large number, so it appears large compared to the original tiny number - but in terms of practical impact, it's SO VERY FAR down the list of approaches to reducing climate change.
A year's worth of smartphone usage will generate about ~5 lbs of CO2. Driving a car ~5 miles (at an average of ~21mpg, or 411 grams CO2/mile) will generate the same CO2.
The average commute in the US is 41 miles round trip - so every day, the average commuter burns 8 years worth of smartphone usage in a CO2 budget by driving their car.
This is getting really back of the napkins-esque (since not all people work/commute) but if we just assume that in general the US population is driving - at ~330 million people, times 8... we get 2.63 billion.
Basically - each day, driving in the US is generating close to the same CO2 that all 3 billion of those smartphone users will generate in a YEAR.
Looks like roughly 1/3 of US pop actually commutes, so we'll be generous and say that every 3 days, we blow through the yearly carbon generation for ALL 3 billion of those smartphone users.
It's just a really, really tiny number compared to other initiatives. You're MUCH better off tackling basically anything else. There is SO much better low hanging fruit.
A week long "don't drive" mandate in the US earns the whole world years of smart phone usage.
Go argue against "back to the office" policies instead - you'll do far more good.
A phone with a 5000mAh battery (more than any iPhone) takes about 20 watt hours of power to charge.
Charging it from empty to full each day would use about 7.3 kWh per year.
Electricity costs about 15c per kWh.
The last good data I can find (2019) puts the average right around $0.90/year for US based phone users.