Encroaching Dragonstorm enters the battlefield, its first ability triggers, causing you to search your library for two basic land cards and put them onto the battlefield tapped.
When the lands enter the battlefield,
Nesting Dragon triggers twice.
Resolve the first trigger, creating a 0/2 Dragon Egg creature token.
When the Dragon Egg enters the battlefield,
Encroaching Dragonstorm's second ability triggers, returning it from the battlefield to your hand.
Resolve the second
Nesting Dragon trigger, creating a 0/2 Dragon Egg creature token.
Activate
Phyrexian Altar twice by sacrificing both Dragon Eggs, adding ({1} magic symbol) ({G} magic symbol) .
When the Dragon Eggs die, they trigger, creating two 2/2 Dragon creature tokens.
Activate
Phyrexian Altar twice by sacrificing both Dragon tokens, adding ({2} magic symbol) .
Repeat.
Results
Put all basic lands from your library onto the battlefield tapped.