neighbor: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/phylip/bin/neighbor - from package: phylip

You may install the required package with command apt-get install {package}

Error in other languages:
neighbor: bevel nie gevind nie
neighbor: comandă negăsită
neighbor: comando não encontrado
neighbor: commande introuvable
neighbor: command not found
neighbor: käsku ei ole
neighbor: không tìm thấy lệnh
neighbor: komanda nerasta
neighbor: Kommando nicht gefunden.
neighbor: kommandot finns inte
neighbor: komut yok
neighbor: nie znaleziono polecenia
neighbor: níor aimsíodh an t-ordú
neighbor: no se encontró la orden
neighbor: no s'ha trobat l'ordre
neighbor: opdracht niet gevonden
neighbor: parancs nem található
neighbor: perintah tidak ditemukan
neighbor: príkaz nenájdený
neighbor: příkaz nenalezen
neighbor: команда не найдена
neighbor: командата не е открита
neighbor: 命令找不到
neighbor: コマンドが見つかりません