What is the shortest form of Salat on the Prophet, peace and blessings be upon him, and is this short form sufficient to attain the intercession of the Prophet, peace and blessings be upon him, if it is recited ten times in the morning and in the evening?

The least that can be said in supplication for the Prophet (peace and blessings of Allah be upon him) is "صلى الله عليه وسلم" (peace and blessings of Allah be upon him). The supplication is valid with any wording, but the best form is the Ibrahimiyyah supplication (Salat al-Ibrahimiyyah) that is mentioned in the Tashahhud.