According to

Why is it important to reduce energy consumption? (2019)

or

How Does Saving Energy Help The Environment (2019)

we can reduce global warming impact when we reduce our energy consumption.

The less power you comsume the more you’ll contribute to a better world!

This applies to all our actions that we perform in our daily lives.

If we drive a heavier car, we need more energy for acceleration and braking than if we were driving a lighter car (see Vehicle Weight | Natural Resources Canada - 2018).

We can save energy and money by buying a lighter car (It also depends on the engine, the driving style and many other factors...).

For devices in general, among other things, the following periods of energy consumption during the lifetime of the device must be considered (in this case it's assumed to be a zero emission device; the energy consumption for design / creation is neglected):

1. The sum of energy needed for device manufacture and assembly
2. The sum of energy needed during the lifetime of the device
3. The sum of energy needed to dismantling, recycling and disposal after lifetime

In the example of smartphone we can improve the energy balance if we use the device as long as possible, because then 1) and 3) is less often needed to invest and 2) is a comparatively small value compared to the others.

As per the article here: Graue Energie – unsichtbar, aber folgenschwer, the smartphone requires a lot of energy to produce in relation to use.

We therefore need to keep the Smartphone as long as possible.

To increase the life of the battery in your smartphone, you need to charge it properly. If you own a lithium-ion battery, you can follow these guidelines according to the article Schont Akku und Nerven: So laden Sie Ihr Handy richtig (2021) (needs to be verified with the manufacturer of the device):

• load as seldom as possible
• do not charge overnight
• avoid extreme temperatures
• start loading at 20% and load up to 80%
• avoid fast loading

The topic ethical responsibility like working conditions of the employees in the production (resource extraction and assembly) would also have to be discussed. Please see this information:

https://www.wwf.ch/sites/default/files/doc-2018-08/2018-07_lehrmittel_lernvideo%20smartphone_begleitdokumentation_0.pdf

or

https://www.youtube.com/watch?v=veVNd9xCqIs

There are many other examples of energy saving possibilities.