Is it inadvisable to analyze or play long chess games on a smartphone? I play a lot of online chess, but I am a federated player whose objective is to play well over-the-board games with 3D pieces.

During my hourly tactics exercises I turn on the computer and do it in the big screen because my results are better than on the smartphone.

For timed games I also play with the PC, as I am quicker with the mouse than with the finger.

But I also play correspondence daily; I use to have 20 games in progress. 

I am getting used to analyze and make the moves on my smartphone, when I am not at home, or when I feel too much lazy to turn on the computer.

I know the best is to analyze on a physical chess board, which I sometimes do on correspondence when the position is interesting. 

But my question is if I should be less lazy and turn on the computer when analyzing deeply with the analysis board.

I know, in deep, this is a neurology question, but at neurosciences SE they would say it is a question for a chess teacher or highly rated player as there are not specific neurology studies on it. 

Just asking, as a 7 years old student could ask: "Teacher, should I always play on the PC or I can use my smartphone playing on the free net?"
Advisable to use smartphone?  Not really. Okay occasionally if you must look at a position. 

As you noted a PC is more helpful to seeing the board and planning your moves.  

I have found no difference between using PC screen adjusted to my preferences and using a real chessboard with physical items on it.
For me the difference between chess sets and boards is more than the difference between my preferred set and board and the PC screen with my choice of size and font. 

Note that moving the men on your phone or pc will negate any OTB experience for a tournament that you would get by analyzing without moving them to improve your analysis vision for 'real' chess in an OTB tournament.