The best list of smartphones up to 400€ is presented by Techstage in this article

The best list of smartphones up to 400€ is presented by Techstage in this article: https://www.techstage.de/bestenliste/Ratgeber-Die-besten-Smartphones-bis-400-Euro-4656083.html?wt_mc=ko.red.ho.conrad-nl.2020-12-08.link.link
 To ensure that you buy a safe smartphone that you can take on an aircraft also or that you can ship as a present, keep the following in mind:

The best list of smartphones up to 400€ is presented by Techstage in this article:
https://www.techstage.de/bestenliste/Ratgeber-Die-besten-Smartphones-bis-400-Euro-4656083.html?wt_mc=ko.red.ho.conrad-nl.2020-12-08.link.link

To ensure that you buy a safe smartphone that you can take on an aircraft also or that you can ship as a present, keep the following in mind:
If you have chosen a smartphone, check with the retailer or the manufacturer before purchase to ensure that all legal requirements have been met by the manufacturer with regard to the lithium ion cell. This is because lithium cells are dangerous goods and are subject to strict regulations to ensure safety in handling and transport.

And every lithium cell and lithium battery must have been manufactured according to a quality management program described in the transport regulations and must have successfully passed the UN Test Series 38.3 of the UN Manual of Tests and Criteria.
How do you get the information?

It is normally NOT supplied with the equipment, as it must only be supplied ON REQUEST. Therefore, you must ask and be patient and sometimes persevere.
Ask the supplier or manufacturer! Good suppliers can present these confirmations and are aware of their duty to provide these confirmations to customers on demand.

The easiest way to do so, is, to use our free-of-charge supplier check list, which also checks all information required by the UN 38.3 test results summary. We have drawn up separate lists, one for lithium cells and one for lithium batteries. You can download them free of charge in German and English under the following link:

https://www.lithium-batterie-service.de/en/downloads-guest

Once you have received the information, you can take the smartphone with you on air travel or ship it.
Especially when traveling by air, you are also subject to restrictions as a passenger when carrying lithium batteries in your luggage.
As passenger in air traffic you are subject to restrictions on dangerous goods you carry with you.
Here you can find out which dangerous goods containing lithium cells or batteries you can take with you on your air travel - in your carry-on baggage, on your own body or in checked baggage:
https://www.lithium-batterie-service.de/en/passengers-travelling-on-aircrafts/

If you're wondering what the UN 38.3 test series is all about, you can find the answer in our Lithium Battery Service Portal at:
https://www.lithium-batterie-service.de/en/un-38.3-test-series

And more on the Quality Management Program you can find here:
https://www.lithium-batterie-service.de/en/quality-management-program