Delaying your turn and Sacrificing Initiative

Can you delay your turn and take it later in the round?

No. When it’s your turn, either you do something or you don’t. If you don’t want to do anything, consider taking the Dodge action so that you’ll, at least, have some extra protection. If you want to wait to act in response to something, take the Ready action, which lets you take part of your turn later.

For a variety of reasons, we didn’t include the option to delay your turn:

• Your turn involves several decisions, including where to move and what action to take. If you could delay your turn, your decision-making would possibly become slower, since you would have to consider whether you wanted to take your turn at all. Multiply that extra analysis by the number of characters and monsters in a combat, and you have the potential for many slowdowns in play.
• The ability to delay your turn can make initiative meaningless, as characters and monsters bounce around in the initiative order. If combatants can change their place in the initiative order at will, why use initiative at all? On top of that, changing initiative can easily turn into an unwelcome chore, especially for the DM, who might have to change the initiative list over and over during a fight.
• Being able to delay your turn can let you wreak havoc on the duration of spells and other effects, particularly any of them that last until your next turn. Simply by changing when your turn happens, you could change the length of certain spells. The way to guard against such abuse would be to create a set of additional rules that would limit your ability to change duration. The net effect? More complexity would be added to the game, and with more complexity, there is greater potential for slower play.

Two of our goals for combat were for it to be speedy and for initiative to matter. We didn’t want to start every combat by rolling initiative and then undermine turn order with a delay option. Moreover, we felt that toying with initiative wasn’t where the focus should be in battle. Instead, the dramatic actions of the combatants should be the focus, with turns that happen as quickly as possible.

That's from the Sage Advice Compendium.

It's pretty much just what Pantagruel said, only with a bunch more words.