UTXO Choice: How does a pockets determine which utxo to make use of?

I’m utilizing a chilly pockets and made a number of tx two days in the past. Nevertheless, although what I needed to ship was a really small quantity of btc, the pockets made a number of utxo of giant quantities become involved and now all my property are locked up because the tx are unconfirmed.
Questions;
- Why does a pockets have to make use of a number of utxo (enter>output 2>2 or 3>2) somewhat than simply use one and cut up it in two (1>2)? (the aimed tx quantity is smaller than every utxo)
- Is the algorithm to pick out which utxo particular to every pockets or is there any normal rule all through bitcoin community?