The official guide in elixir site is not up-to-date.

Install Erlang (extract from https://elinux.org/Erlang)

sudo apt-get update
sudo apt-get install wget
sudo apt-get install libssl-dev
sudo apt-get install ncurses-dev
wget http://www.erlang.org/download/otp_src_24.0.tar.gz
tar -xzvf otp_src_24.0.tar.gz
cd otp_src_24.0/
./configure
make
sudo make install
cd ..
rm otp_src_24.0.tar.gz
sudo rm -R otp_src_24.0/

Install Elixir from source:

wget https://github.com/elixir-lang/elixir/archive/v1.12.3.tar.gz
tar -xvzf v1.12.3.tar.gz
make install

Please install elixir v1.11.x for phoenix 1.5.x

Refernece: https://github.com/elixir-lang/elixir-lang.github.com/issues/1510#issuecomment-830746952

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