source = [
    'Sergeev', 'Artem', '+70000000000',
    'Ivanova', 'Anna', '+70000000000',
    'Sidorova', 'Arina', '+70000000000',
    'Gavrilov', 'Vitalik', '+70000000000',
    'Petrov', 'Viktor', '+70000000000',
]

result = dict()
for i in range(0, len(source), 3):
    result[source[i]] = (source[i+1], source[i+2])

print(result)

{
    'Sergeev': ('Artem', '+70000000000'),
    'Ivanova': ('Anna', '+70000000000'),
    'Sidorova': ('Arina', '+70000000000'),
    'Gavrilov': ('Vitalik', '+70000000000'),
    'Petrov': ('Viktor', '+70000000000')
}